It is known that the triazolyl styryl ketone derivative (I) itself is useful as an antimicrobial agent [cf. Japanese Patent First Publication (Kokai) No. 130661/1978], and that triazolyl styryl carbinol of the formula (II): ##STR4## which is obtained by reduction of the above derivative (I), is more useful as an antimicrobial agent, a herbicide, a plant growth regulator, or the like. It is also known that the effect of E-isomer thereof is particularly superior to that of the Z-isomer [cf. Japanese Patent First Publication (Kokai) No. 41875/1979, 124771/1980 and 25105/1981].
Accordingly, it is desired to provide a process for efficiently preparing the E-isomer of the triazolyl styryl ketone dirivative of the above formula (I) which is a starting material for preparing the E-isomer of the above compound of the formula (II) (hereinafter E-isomer, Z-isomer and a mixture of E-isomer and Z-isomer of the triazolyl styryl ketone derivative (I) are simply referred to as "E-isomer", "Z-isomer" and "E/Z-isomer", respectively, unless specified otherwise). As a process for satisfying such a requirement, for example, the following processes are proposed:
(1) A process of isomerizing Z-isomer or E/Z-isomer into E-isomer with light [cf. Japanese Patent First Publication (Kokai) No. 147265/1980].
(2) A process of isomerizing Z-isomer or E/Z-isomer with a compound such as an aromatic mercaptan [cf. Japanese Patent First Publication (Kokai) No. 147265/1980].
(3) A process of separating E/Z-isomer with chromatography [cf. Japanese Patent First Publication (Kokai) No. 147265/1980].
(4) A process of separating E-isomer from E/Z-isomer, which comprises treating E/Z-isomoer with sulfuric acid, precipitating and separating the sulfuric acid salt of E-isomer, and decomposing the salt to obtain E-isomer [cf. Japanese Patent First Publication (Kokai) No. 140081/1983].
However, these processes have problems such as, for example, the necessity of a special reaction apparatus or the necessity of an additional treatment for separating E- and Z-isomers from the reaction products because of an insufficient isomerization rate. Moreover, in the case of the process for merely separating E-isomer from E/Z-isomer such as the process (4), the yield of E-isomer is dependent on the E-isomer content contained in the starting E/Z-isomer and the treatment of the residual Z-isomer is also necessary.